Decreasing Al Concentration Research Articles

Microstructure, Mechanical Properties and Thermal Stability of Ni-Based Single Crystal Superalloys with Low Specific Weight

Ni-based single crystal (SX) superalloy with low specific weight is vital for developing aero engines with a high strength-to-weight ratio. Based on an alloy system with 3 wt.% Re but without W, namely Ni-Co-Cr-Mo-Ta-Re-Al-Ti, a specific weight below 8.4 g/cm3 has been achieved. To reveal the relationship among the composition, mechanical properties, and thermal stability of Ni-based SX superalloys, SXs with desirable microstructures are fabricated. Tensile tests revealed that the SX alloys have comparable strength to commercial second-generation SX CMSX-4 (3 wt.% Re and 6 wt.% W) and Rene′ N5 alloys (3 wt.% Re and 5 wt.% W) above 800 °C. Moreover, the elongation to fracture (EF) below 850 °C (>20%) is better than that of those two commercial SX superalloys. During thermal exposure at 1050 °C for up to 500 h, the topological close-packed (TCP) phase does not appear, indicating excellent phase stability. Decreasing Al concentration increases the resistance of γ′ rafting and replacing 1 wt.% Ti with 3 wt.% Ta is beneficial to the stability of the shape and size of γ′ phase during thermal exposure. The current work might provide scientific insights for developing Ni-based SX superalloys with low specific weight.

Influence of soil geomorphic factors on vegetation patterns in a model white sands ecosystem complex

Understanding the development of white sands ecosystems (WSEs) and their occurrence is critical for determining structural diversity in global biodiversity hotspots. WSE has fascinated ecologists for decades, with soil always opined to play a critical role in the development of complex ecosystem vegetation patterns. However, few to no studies have systematically investigated the effect of soil natural capital on the complex vegetation patterns in humid tropical forests that include the occurrence of open savannas. Instead, fires have been advanced as the key driver that sustains and expands open savannas in tropical forest biomes. In this study, we investigated the effects of soil geomorphic factors on vegetation patterns that range from tropical forests to open savannas in a model WSE complex known as the Aripo savannas scientific reserve. Soils were sampled from three white sands landscapes, each containing three vegetation types (open savanna, palm island, and marsh forest). Two transects of five soil sampling sites were randomly sampled in each vegetation type where stratified sampling of microtopography (hollows and flats) was applied. Samples were analyzed mainly for chemical properties, with some physical and mineralogical properties. Results showed patterns and relationships amongst vegetation types. Parent material was rich in quartz and zircon, poor in alkalis and sesquioxides, and resistant to weathering, forming white sands. Open savannas were significantly higher (P < 0.05) in coarse silt (32.8 %) and fine sand (34.1 %) and lower in fine silt and clay, suggesting a clear sorting associated with aeolian cover sands. In microtopographic areas, the upward gradient of water potential drove matter accumulation in hollows and upward translocation of elements under flat relief. The plant available nutrients and carbon were significantly lower (P < 0.05) in open savannas, demonstrating that plant nutrition was resource dependent. The Al concentration and pH matched with the vegetation patterns with a significantly decreasing Al concentration from forests (953 ppm) to open savannas (223 ppm) and significantly increasing pH from forests (3.7) to open savanna (4.1). Interestingly, the significantly lower Al concentration and higher pH in the open savanna suggest that these properties though more favorable in this locale, did not support tree growth and therefore were not predominant determinants of vegetation patterns. Quartz dominated all textural fractions, with clay fractions (which increased under forest) having higher levels of non-quartz minerals, e.g., silica. Silica, which is more degradable and initially provided more cations (nutrients and Al) to forest vegetation. Therefore, both texture (clay size) and minerals (clay minerals) together, degraded and delivered more cations. We conclude that WSEs in tropical forests developed on originally poor parent material. Since natural fire regimes are unlikely in this ecosystem, differences in vegetation distribution were not attributable to fires but are related to soil variability due to weathering and pre- weathering sorting. Most likely matter transport by lateral sheet water flow due to soil geomorphology is another factor controlling the development of vegetation patterns within WSE mainly found in humid tropical areas where wet season rainfall exceeds 2000 mm.

Optimization of heat treatment condition of nonflammable Mg-Al-Ca alloys with high thermal conductivity

Our previous study found that the thermal conductivity of nonflammable Mg-Al-Ca alloys is improved by heat treatment. Heat-treated Mg-Al-Ca alloys exhibited a high thermal conductivity of 100–130 W m−1 K−1 because of C15 (Al2Ca) compound precipitation in the α-Mg phase. In this study, the optimal heat treatment condition and the effect of C15 precipitation behavior on thermal conductivity were investigated using Mg91.98Al5Ca3Mn0.02 alloys. The thermal conductivity saturated at approximately 120 W m−1 K−1 in the shortest time at a heat treatment temperature of 673 K. This suggests that the nucleation rate of the C15 compounds could reach the highest at 673 K. Through the formation of dense, long, and thick C15 compounds, thermal conductivity increased with decreasing Al concentration in the α-Mg matrix.

Elevated CO2 improves phosphorus nutrition and growth of citrate-secreting wheat when grown under adequate phosphorus supply on an Al3+ -toxic soil.

Understanding how climate change affects the phosphorus (P) nutrition of crops grown on acid soils is important in optimizing the management of P, and to secure future food production on these soils. This study assessed the impact of elevated CO2 (eCO2 ) on the P nutrition of wheat (Triticum aestivum) grown on Al3+ -toxic and P-deficient soils or in hydroponics. The aluminium-resistant near-isogenic wheat lines EGA-Burke (malate efflux only) and EGA-Burke TaMATE1B (malate and citrate efflux) were grown under ambient (400 μmol mol-1 ) and elevated CO2 (800 μmol mol-1 ) in growth chambers for 4-6 weeks. Elevated CO2 enhanced shoot growth and total P uptake of both lines at P rates >250 mg kg-1 , which was associated with improved root biomass allocation and thus increased root growth, but these effects were not apparent at lower P rates. Elevated CO2 decreased specific P uptake (P uptake per unit root length) at P supply >250 mg kg-1 , but did not significantly affect external or internal P requirements. This effect on the specific P uptake was less for EGA-Burke TaMATE1B than for EGA-Burke, possibly due to the increased citrate efflux and decreased Al concentration in root tips of EGA-Burke TaMATE1B. Compared to EGA-Burke, citrate-exuding EGA-Burke TaMATE1B had greater shoot P concentration and greater specific P uptake. Elevated CO2 improved root growth, and thus total P uptake and plant production of both lines when high P alleviated Al3+ toxicity and improved P nutrition in acid soils. The decreased P uptake efficiency under eCO2 was less for EGA-Burke TaMATE1B than EGA-Burke. © 2022 Society of Chemical Industry.

Melatonin alleviates aluminum-induced growth inhibition by modulating carbon and nitrogen metabolism, and reestablishing redox homeostasis in Zea mays L.

Melatonin, a regulatory molecule, performs pleiotropic functions in plants, including aluminum (Al) stress mitigation. Here, we conducted transcriptomic and physiological analyses to identify metabolic processes associated with the alleviated Al-induced growth inhibition of the melatonin-treated (MT) maize (Zea mays L.) seedlings. Melatonin decreased Al concentration in maize roots and leaves under Al stress. Al stress reduced the total dry weight (DW) by 41.2% after 7 days of treatment. By contrast, the total DW was decreased by only 19.4% in MT plants. According to RNA-Seq, enzyme activity, and metabolite content data, MT plants exhibited a higher level of relatively stable carbon and nitrogen metabolism than non-treated (NT) plants. Under Al stress, MT plants showed higher photosynthetic rate and sucrose content by 29.9% and 20.5% than NT plants, respectively. Similarly, the nitrate reductase activity and protein content of MT plants were 34.0% and 15.0% higher than those of NT plants, respectively. Furthermore, exogenous supply of melatonin mitigated Al-induced oxidative stress. Overall, our results suggest that melatonin alleviates aluminum-induced growth inhibition through modulating carbon and nitrogen metabolism, and reestablishing redox homeostasis in maize.Graphical Abstarct [Display omitted]

Liming effect of non-legume residues promotes the biological amelioration of soil acidity via nitrate uptake

The utilisation of on-farm crop residues to ameliorate soil acidity is thought to be more cost-effective than other organic materials such as animal manures. In addition, using NO3− as the form of N can induce rhizosphere alkalinisation due to the excess uptake of anions over cations by plant roots. A pot experiment was conducted to evaluate the effectiveness of four commonly-used brown manures, field pea, oats, vetch and wheat in combination with two Ca(NO3)2 levels (64 and 191 mg N kg− 1) in improving wheat growth in two acid soils varying in Al3+ concentration and pH buffer capacity. All amendments increased plant growth and soil pH, and decreased Al concentration in Sodosol (pH buffer capacity, 23 mmolc kg− 1 pH− 1), with legume residues (field pea and vetch) being more effective than cereal residues (oat and wheat). Application of Ca(NO3)2 alone was less effective in ameliorating soil acidity in both Sodosol and Dermosol due to poor root growth and hence lower NO3−-N uptake ( 52) could act as an alternative to costly lime or off-farm products in ameliorating soil acidity.

Structural, infrared and magnetic properties of MgAlxFe2-xO4 compounds: Effect of the preparation methods and Al substitution

Aluminum substituted magnesium ferrite MgAlxFe2-xO4 (x = 0.0, 0.2, 0.3, 0.7 and 2.0) are prepared by two commonly-used methods: Sol-gel (SG) and Solid-phase reaction (SR). Structural studies are carried out using X-ray and neutron diffraction, and FTIR techniques, and heat generation ability in the AC magnetic field is explored by the specially designed device. Diffraction patterns revealed the formation of single cubic spinel MgAlxFe2-xO4 ferrites for SG and additional MgAl2O4 phases at higher concentration of aluminum (x > 0.3) in SR samples. Structural studies are carried out using X-ray and neutron diffraction, and FTIR techniques, scanning electron microscopy (SEM) and heat generation ability in the AC magnetic field is explored by the specially designed device. This study attempts to compare both chemical methods, and to correlate the properties with Al substitution concentration. Diffraction patterns revealed the formation of single cubic spinel MgAlxFe2-xO4 ferrites for SG and additional MgAl2O4 phases at higher concentration of aluminum (x > 0.3) in SR samples FTIR was used to confirm the spinel structure, the main vibrating modes were observed to shift to higher wave number with increasing Al3+ concentration. The tetrahedral force constant (KT) increases continuously with Al3+ concentration. The morphology investigations revealed the spherical morphology of particles with some agglomeration. The heat-generation ability was enhanced with decreasing Al concentration. Upon exposure to an external alternation magnetic field of 70 kHz and intensity of 54.3 mT, specific power absorption rate (SAR) of the Magnesium ferrite aluminates. The heat generation ability of the MgAlxFe2-xO4-SR ferrites are higher than those of MgAlxFe2-xO4-SG samples. Moreover, doping element is affected to cation distribution between tetrahedral and octahedral sites. For MgAlxFe2-xO4, heat generation ability will be influenced by additional magnetic properties and cation distribution. This will be distinguished by more detailed investigation for magnetic properties.

Slow movement of alkali from surface-applied lime warrants the introduction of strategic tillage for rapid amelioration of subsurface acidity in south-western Australia

Conventional surface-application of agricultural lime takes many years to increase pH deeper in the soil profile, which is a barrier to increased adoption of liming. We conducted a series of experiments to measure the rate of vertical movement of alkali and identify the factors that determine this movement into the subsurface, to evaluate the feasibility of ameliorating acidic subsurface soil using residual (undissolved) lime (CaCO3) at Wongan Hills (30.85°S, 116.74°E) and Merredin (31.48°S, 118.21°E) and to test whether deep tillage and lime incorporation can significantly speed up the amelioration of subsurface soil acidity at Kalannie (30.42°S, 117.29°E). Multiple applications of lime to the surface of the soil at higher rates (total 6–8.5 Mg ha–1) significantly increased subsurface soil pH but only in the 0.10–0.20 m depth by 0.049 pH units per year over 10–24 years. A large proportion of the surface-applied lime was stratified in the top few centimetres of the soil and incorporation of this undissolved lime with a rotary hoe to a depth of 0.25 m significantly increased soil pH (by 0.63 units) within a year in the Wongan Hills field experiment. Deep incorporation of 6 Mg ha–1 lime to a depth of 0.45 m through excavation and spading with a small rotary hoe also increased soil pH by more than a unit and decreased Al concentration to below the toxic level within two months in the Kalannie experiment, allowing wheat (Triticum aestivum L.) plants to produce root systems up to 0.59 m deep compared with 0.26 m for the control. Our soil column leaching experiment indicated that surface incorporation of lime in higher rainfall regions can be useful to treat subsurface soil acidity but that the rate of improvement in subsurface pH was slow. Therefore, deeper incorporation of lime using cost-effective strategic deep tillage is likely to be necessary.

Aluminum Detoxification by Humic Substance Extracted from Compost of Organic Wastes

Aluminum Detoxification by Humic Substance Extracted from Compost of Organic Wastes (S Winarso, E Handayanto and A Taufiq): Humic substance could control the activity of metal as well as exchangeable aluminum (Alexch) on acid soil. The humic substance extracted from compost of agricultural waste is rarely conducted. The objective of research was to evaluate the effect of humic substance concentration and sources to pH and Al suspension. The research had been conducted in the Soil Laboratory of Agricultural Faculty of Jember University from April to July 2009. The humic substance used in these researches was extracted from compost of rice straw (RS), soybean straw (SS), cassava starch solid waste (CSSW), and empty bunch of oil palm tree (EBOPT). The humic substance concentration treatments were 0, 10, 20, 30, 40, 50, 75, 100, 150, 200, 250, and 300 ppm. Result of the analysis showed that characteristic of humic substance was difference depending on the source material used. The humic substance extracted from SS contain total base cations (K, Na, Ca, Mg) higher (1.17%) compared with CSSW (1.07%), OPT (0.87%), and RS (0.69%). While the humic substances extracted from RS contain total organic acid (Acetic, Fumeric, cetoglutamic, Sucsinic, Propionic, Butiric, Ocsalic, and sitric acid) higher (157 ppm) compared with EBOPT (129 ppm), SS (115%), and CSSW (108%). Among these organic acids, acetic acid was highest concentration (&gt; 34.51% of total acid). The addition of humic substance increased pH and decreased aluminum concentration of the suspension. The higher pH increment and Al concentration reduction took placed in the suspension treated with humic substance from SS compost. The correlation between decreasing Al concentration with humic substance concentration which explained chelation was higher (r = 0.97) than decreasing Al concentration with increasing pH which explained precipitation (r = 0.93). Based on these research results, it can be concluded that humic substance extracted from agricultural waste have a good prospect as a soil ameliorant to increase soil pH, detoxify soil aluminum, and increase soil P availability on acid soil.

Relating coke formation and characteristics to deactivation of ZSM-5 zeolite in methanol to gasoline conversion

Two ZSM-5 catalysts, differing only in their crystal size, viz, nanocrystal at∼100nm and microcrystal at 13μm, respectively, were synthesised and tested in methanol to gasoline (MTG) conversion, with a focus on the formation and characteristics of coke deposits. Over time periods when methanol conversion decreased to 50%, herein termed as the service lifespan of the catalyst, the nanocrystal catalyst incurred 31.1wt% coke deposition, while the microcrystal counterpart had 14.1wt% coke. The nanocrystal catalyst showed a service lifespan almost seven times longer than the microcrystal catalyst. The difference in the catalytic service lifespans was examined in terms of the rate of formation of internal coke and structural properties of external coke, as determined using nitrogen physisorption, TGA and TEM. It was found that the internal coke was quickly formed in the microcrystal catalyst leading to rapid coverage of the active sites and blockage of the pores, resulting in fast deactivation. In contrast, coke formed preferentially on the external surface in the case of the nanocrystal catalyst. This external coke was of porous graphitic structures, and thus was not detrimental to the catalytic performance. The coke fouled nanocrystal catalyst was regenerated and the activity of the regenerated catalyst was evaluated under the same reaction conditions. An increase in catalytic service lifespan compared to the pristine nanocrystal catalyst was observed, due to the effect of decreased Al concentration on the catalytic performance.

Influence of alloy composition and thermal history on carbide precipitation in γ-based TiAl alloys

Carbide precipitation in TiAl alloys with different alloying element additions and thermal history was investigated by transmission electron microscopy and high energy X-ray diffraction. The results reveal that Nb addition in TiAl alloys does not increase the carbon solubility in the γ matrix significantly. With increasing carbon concentration in the alloys, a splitting of the P-type carbides takes place earlier in the course of ageing at 800 °C and the formation of H-type carbides is promoted. For a nearly single γ phase alloy Ti51Al5Nb0.5C, H-type carbides are the thermodynamically stable phase. However, with decreasing Al concentration, P-type carbides become thermodynamically stable at low carbon concentration (below 1%) in Ti45Al and Ti45Al5Nb alloys. It is feasible to achieve high thermodynamical stability of the P-type carbides in TiAl alloys through controlling alloying elements.

Effects of foliar application of organic acids on alleviation of aluminum toxicity in alfalfa

AbstractOrganic acids (OA) may affect plant resistance to aluminum (Al) toxicity in acidic soils. However, limited information is available on the effects of different organic acids on Al resistance in alfalfa. We investigated the effects of foliar application of organic acids (succinic acid, citric acid, malic acid, and oxalic acid) to alfalfa (Medicago sativa L.) under Al stress. Seedlings were grown in pH 4.5 nutrient solution containing Al at 0 or 100 μM, and were sprayed with water or 100 μM of oxalic acid, malic acid, citric acid, or succinic acid every 3 d during a 10 d experiment. Aluminum stress caused significant reduction in alfalfa growth (reflected by above‐ground biomass, root weight and root length), root activity, mineral nutrient concentrations (Ca, K, Mg, Mn and Zn), and a significant increase in leaf membrane lipid peroxidation. Foliar application of the four organic acids, especially succinic acid, alleviated Al toxicity, as demonstrated by the increase in plant growth and root activity, as well as reduction in lipid peroxidation. Oxalic acid and malic acid treatments significantly increased oxalate exudation and decreased Al concentration in roots exposed to Al stress. Succinic acid treatment significantly increased accumulation of all four organic acids in roots, accumulation of Ca, K, Mg, Mn and Zn, and up‐regulated the gene transcription of malate dehydrogenase (MDH) and phosphoenolpyruvate carboxylase (PEPC) in roots. Our results suggest that the promotion of oxalate exudation from roots through exogenous application of oxalate and malate could contribute to the improvement in Al resistance of alfalfa, and the positive effects of exogenous application of succinate on Al resistance may be associated with the increased endogenous accumulation of all four organic acids in roots, which may constitute an organic‐acid detoxification system in alfalfa.

Al–Cr–Fe phase diagram. Isothermal Sections in the region above 50 at% Al

The Al–Cr–Fe phase diagram was studied in the compositional range of 50–100at% Al and partial isothermal sections were determined at 1160, 1100, 1075, 1042, 1000, 900, 800 and 700°C. In the low-Al part of the studied compositional region the isostructural high-temperature Al–Cr and Al–Fe γ1-phases form a continuous region of solid solutions. Both binary Al13Fe4 and Al5Fe2 were found to dissolve up to 6.5at% Cr while Al2Fe was found to extend up to 4.1at% Cr. The solid solutions based on the Al–Cr γ2 and μ phases were determined to reach 35.2 and 1.3at% Fe, respectively. The dissolution of Cr in the Al–Fe binaries only slightly influences their Al concentrations, while the Al–Cr binaries exhibit decreasing Al concentration with increasing Fe concentration. The Al–Cr η-phase dissolves up to 5at% Fe, which results in a sharp decrease of its Al concentration and increase of melting temperatures. The earlier reported existence of a ternary decagonal D3-phase and three complex periodic phases O1, H and ε was confirmed and their compositions at different temperatures were specified.

Effect of Al content on the microstructure and mechanical behavior of two-phase FeNiMnAl alloys

The effects of varying the Al content in the range of 11–15 at.% on the microstructure and room-temperature mechanical properties of lamellar-structured FeNiMnAl alloys with compositions close to Fe30Ni20Mn35Al15 have been studied, and the temperature dependence of the yield strength of one composition, i.e., Fe36Ni18Mn33Al13, has been investigated. All alloys consisted of B2 and fcc phases. Decreasing the Al content initially (13 and 14 at.% Al) led to marked increases in both the fcc phase fraction and fcc lamellar spacing, λ, but, on further reducing the Al content (11 and 12 at.% Al), the lamellar structure was no longer present. The elongation to fracture of the FeNiMnAl alloys increased with the decreasing Al concentration from 6.5 % at 15 at.% Al to 31.1 % at 11 at.% Al with a concomitant decrease in the yield stress from 820 to 255 MPa. For the lamellar-structured alloys, the yield stress, σy, obeyed a Hall–Petch-type relationship with λ, i.e., \( \sigma_{y } = \sigma^{\prime}_{0} + k^{\prime}\lambda^{ - 1} \), where \( \sigma^{\prime}_{0} \) is the lattice resistance, and k′ is a constant. The compressive yield stress of Fe36Ni18Mn33Al13 was found to be independent of temperature up to 700 K, after which it decreased dramatically because of the softening of the B2 phase. All alloys showed ductile fracture modes.

Effects of advanced oxidation pretreatment on residual aluminum control in high humic acid water purification

Due to the formation of disinfection by-products and high concentrations of Al residue in drinking water purification, humic substances are a major component of organic matter in natural waters and have therefore received a great deal of attention in recent years. We investigated the effects of advanced oxidation pretreatment methods usually applied for removing dissolved organic matters on residual Al control. Results showed that the presence of humic acid increased residual Al concentration notably. With 15 mg/L of humic acid in raw water, the concentrations of soluble aluminum and total aluminum in the treated water were close to the quantity of Al addition. After increasing coagulant dosage from 12 to 120 mg/L, the total-Al in the treated water was controlled to below 0.2 mg/L. Purification systems with ozonation, chlorination, or potassium permanganate oxidation pretreatment units had little effects on residual Al control; while UV radiation decreased Al concentration notably. Combined with ozonation, the effects of UV radiation were enhanced. Optimal dosages were 0.5 mg 0 3/mg C and 3 hr for raw water with 15 mg/L of humic acid. Under UV light radiation, the combined forces or bonds that existed among humic acid molecules were destroyed; adsorption sites increased positively with radiation time, which promoted adsorption of humic acid onto polymeric aluminum and Al(OH) 3(s). This work provides a new solution for humic acid coagulation and residual Al control for raw water with humic acid purification.

Weak-beam TEM study on planar fault energies of Al-lean TiAl-base alloys

Weak-beam transmission electron microscope (TEM) analyses of 1/2〈112〉 superdislocations were performed in order to determine the stacking fault energies in Ti–45Al, Ti–49Al, Ti–45Al–10Nb and Ti–49Al–10Nb alloys (at.%) at 900 °C. In Al-lean binary TiAl alloys, the SISF energies decrease significantly with decreasing Al concentration in the γ phase, from 97 mJ m −2 for 49.6% Al to 64 mJ m −2 for 48% Al. The ternary alloys exhibit a relatively low SISF energy of about 68 mJ m −2, which is practically independent of the Al concentration.

Effect of composition on grain refinement in TiAl-based alloys

Grain refinement through boron addition has been investigated in a range of cast TiAl-based alloys. The alloys have 44–50 at.% Al, up to 8 at.% alloying elements, and 1 at.% boron. The observed grain size ranges from 40 to 300 μm. The grain size in as-cast TiAl-based alloys is strongly composition dependent with aluminium having the strongest effect. Decreasing Al concentration from 50 to 44% the grain size can be reduced to 50 from 300 μm with similar casting conditions. Alloying element species and concentration also have strong effect on grain size. The strong boride formers like W, Ta and Nb increase the grain size and change the prevalent titanium boride form from TiB 2 to TiB. It is elucidated that the compositional effect on the grain size could be through affecting the local boron concentration in the solidification front during casting.

The effect of calcium additions on the oxidation behavior in magnesium alloys

Our previous study found that the thermal conductivity of nonflammable Mg-Al-Ca alloys is improved by heat treatment. Heat-treated Mg-Al-Ca alloys exhibited a high thermal conductivity of 100–130 W m−1 K−1 because of C15 (Al2Ca) compound precipitation in the α-Mg phase. In this study, the optimal heat treatment condition and the effect of C15 precipitation behavior on thermal conductivity were investigated using Mg91.98Al5Ca3Mn0.02 alloys. The thermal conductivity saturated at approximately 120 W m−1 K−1 in the shortest time at a heat treatment temperature of 673 K. This suggests that the nucleation rate of the C15 compounds could reach the highest at 673 K. Through the formation of dense, long, and thick C15 compounds, thermal conductivity increased with decreasing Al concentration in the α-Mg matrix.

Effects of Al-concentration and lamellar spacing on the room-temperature strength and ductility of PST crystals of TiAl

The tensile deformation behavior of PST crystals of TiAl with several different compositions (Ti–46–49.3 at.%Al) has been investigated in tension at room temperature as a function of crystal orientation (the angle φ between the lamellar boundaries and tensile axis) and crystal growth rate. The average thickness of TiAl ( γ ) lamellae as well as the average spacing of Ti 3 Al ( α 2 ) lamellae decreases with the decrease in Al-concentration and with the increase in growth rate. The yield stress for all orientations increases with decreasing Al concentration. While the value of tensile elongation for perpendicular ( φ =90°) and intermediate ( φ =31–68°) orientations does not significantly depend on Al concentration, the value for the parallel orientation ( φ =0°) increases with decreasing Al concentration. The observed tensile behavior of these TiAl PST crystals are discussed in terms of microstructural features such as the thickness of both γ and α 2 lamellae, the spacing of α 2 lamellae, the volume fraction of the α 2 phase and γ domain size.

ＳＵＳ３１０Ｓステンレス鋼の機械的性質に及ぼすアルミニウム拡散被覆の影響

A new method has been developed to diffuse aluminum onto austenite stainless steel sheet. In the present study, samples diffused Al onto SUS 310S stainless steel were made by changing the thickness of Al foil attached on the surface of SUS 310S and varying heat treatment conditions. The structural changes in the diffusion layer and the mechanical properties of the samples were then investigated. The diffusion layer consisted of two layers: Layer I was α2 (FeAl) and layer II was a mixed structure of NiAl and α. Kirkendall voids were observed between the two layers. The hardness of layer I increased with increasing Al concentration, which was consistent with that of Fe-Al intermetallic compounds reported by others. That of layer II and the substrate was hardly changed by the aluminized coating. Tensile properties were strongly affected by surface cracks occurring on the diffusion layer during loading. The number of serrations appeared after yielding on the stress-strain curve correlated to that of cracks. The yield strength of layer I was evaluated by rule of mixtures, in which the yield strength had a peak in the vicinity of an Al concentration of 20wt% because of the strengthening mechanism brought about by mixing ordered and disordered phases. The tensile strength and elongation of samples decreased with increasing the thickness of the diffused layer and decreasing Al concentration due to the effect of three-axis stress under the crack tip.